Most pipelines must be assembled from a series of pipe sections abutted end-to-end, and many require that fluid materials, such as liquid chemicals, or fluid-like material, such as fine particulate dust or gases, be conveyed without leakage. Some such fluid materials are conveyed under pressure. In order to avoid leakage, the pipe sections must be coupled in a manner which seals the joint. A coupling for joining two abutting pipe ends may typically include either two semi-cylindrical pieces fastened together to clamp the pipe ends, or a single cylindrical piece having an axial slit which allows the coupling to be opened by an amount sufficient to fit over the pipe ends. A coupling may also be used where a pipe has developed a leak remote from the pipe ends and must be repaired.
Whether the task involves joining pipe sections or repairing pipes, gaskets are used often to seal all possible pathways through which fluid materials might escape from the interior of the pipe sections to the exterior of the pipe coupling. A major portion of the sealing function can be accomplished by placing annular gaskets, such as O-rings, around the respective ends of pipe sections. The O-rings are positioned between the coupling and the outer surfaces of the pipe ends. The pressure of the fit causes the O-rings to change shape, filling the space between the coupling and the outer surfaces of the pipe. In this way, fluid materials are blocked from leaking past the O-rings along the surfaces of the pipe. However, the use of O-rings to minimize leakage presents several problems when pipelines are being repaired. First, placing O-rings around pipe ends may be difficult if there is insufficient room to maneuver the O-rings onto the pipe ends. It is standard practice with O-rings to size them so that their inner diameter is smaller than the outer diameter of the pipe upon which they are to be installed. "Stretching" the O-rings onto the pipe tends to keep the O-rings in place and reduces their tendency to bunch up or to buckle. However, stretching O-rings onto a pipe can be difficult in some situations. In fact, it may be impossible to slide O-rings onto a section of pipe to be repaired without cutting the pipe, removing an entire section of pipe, or otherwise complicating the repair project. If the repair is a leak located between pipe ends, installation of O-rings may be impossible.
Further, positioning O-rings between the coupling and the outer surfaces of the pipe may strain the axial joints of the coupling and allow for leakage through the axial joints. The pressure exerted on the O-rings from their placement between the coupling and the pipe may not be uniform causing the O-rings to buckle and lose their seal. Or, the pressure exerted by the coupling may be transmitted through the O-rings to the pipe, causing cracks.
While O-rings may accomplish a large part of the sealing function, the fluid pathway through the axial joints in the coupling must also be sealed. Generally, axial gaskets have been used to provide a seal along the axial joints. One approach, as shown in U.S. Pat. No. 2,913,262 and U.S. Pat. No. 3,153,550, has been to provide an axial gasket extending between the O-rings within the axial joints of the coupling. A problem with this approach is that the coupling must be precisely closed to effect a reliable seal. An overly tight coupling may deform the seal provided by the gasket assembly and allow for leakage.
Another approach, as shown in U.S. Pat. No. 1,607,943, has been to provide an annular central web connecting the O-rings, completely surrounding the pipe ends and spanning the gap between the pipe ends. This solution has the disadvantage that if the web is physically pressed by the coupling against the pipe ends, sharp or ragged pipe ends may cause damage to the gasket or otherwise cause wear which may lead to early deterioration of the gasket. If the web is not pressed against the pipe ends by the coupling, then the pressure of fluid within the pipes must be relied upon to maintain the seal of the joint. If the diameter of the web does not accurately match that of the pipe, the web may buckle or otherwise deform, thereby defeating its sealing function. This may happen even with known web-type gaskets which include a slanted axial joint. Excess force on the coupling may then be required to close up gaps and form a seal.
Other types of gasket devices used to seal leak locations include repair sleeves and wraparound gaskets. These devices generally include a flat piece of rubber with a waffle pattern that contacts the pipe. A problem with this type of sealing device is that it does not allow for movement or deflection of the pipe ends at the joint or the pipe at a leak location. Deflection of the pipe may break the seal between the waffle material and the pipe.
U.S. Pat. No. 4,360,227 discloses a successful pipe coupling and gasket for solving some of the problems in the art. The gasket includes O-rings joined by a web only in the area of the axial slit of the coupling. Assembly of the preferred embodiment requires molding of the shaped web and vulcanizing or otherwise bonding the web to the O-rings, plus the further attachment of a shield under the web, if desired. Installation on pipe ends requires that the pipe ends be held together while stretching both O-rings over the adjacent pipe ends, and while the coupling is fitted over the gasket and pipe ends. A disadvantage of this approach is that in some installations it is difficult to get the web and O-ring assembly to stay in place on the pipe ends during installation of the coupling. In addition, positioning the web against the O-rings and fitting the coupling over both may deform or buckle the O-rings and affect the seal that they provide, thereby permitting leakage.
Another approach for sealing the axial joint of a coupling is described in U.S. Pat. No. 4,664,428, which describes a sealing plate spanning the axial slit of the coupling member. The sealing plate carries on its upper surface a pair of axial gaskets which seal against the coupling above the sealing plate and against O-rings on the pipe sections below the sealing plate. U.S. Pat. No. 4,664,428 also describes a sealing gasket extending along an axial edge of the coupling so that the gasket is positioned between the axial edge and the inner surface of the coupling when the coupling is fixed around the pipe. Both approaches described in U.S. Pat. No. 4,664,428 have the common disadvantage shared by the previously described prior art, that is, that in fitting the pipe coupling over the O-rings and other gaskets, the O-rings may buckle, deform, or be displaced, thereby allowing leakage.
Thus, there is a need in the art for a means to seal a leak location in a pipe quickly and easily without expensive equipment or a high degree of skill for installation. Further, there is a need in the art for a pipe coupling that reliably seals all fluid paths from the interior of the pipe sections to the exterior of the pipe coupling. In particular, there is a need in the art for a means to seal the axial joint of a pipe coupling without deforming the seal provided by O-rings and axially extending gasket material positioned between the pipe coupling and the outer surfaces of a pipe. There is also a need for such a pipe coupling made of stainless steel, but which is lightweight and for use in connection with low to moderate pressure pipes.